The present invention relates to a plasma processing apparatus for carrying out plasma processing on work objects such as substrates and the like.
Plasma processing is commonly known as a method of surface treatment like cleaning and etching of work objects such as substrates and the like on which electronic components are mounted. To accomplish a desired surface treatment, a method of plasma processing includes:
(A) placing a substrate to be processed in a vacuum chamber constituting a processing chamber;
(B) supplying processing gas into the processing chamber after the chamber has been evacuated to a vacuum state;
(C) generating plasma within the processing chamber maintained under a predetermined pressure; and
(D) bombarding a surface of the substrate with generated ions and/or electrons to finish the surface treatment of the substrate.
A gas importing unit for delivering the processing gas requires a gas flow-rate regulating function in order cause a predetermined amount of the processing gas to flow continuously, and a commercially available mass flow controller is used generally for this purpose.
A mass flow controller comprises:
(a) a flow control valve with an adjustable orifice in a gas passage;
(b) a flow rate detector for detecting a flow rate in the gas passage; and
(c) a feedback controller for comparing a fed-back result of detected flow rate with a previously directed flow-rate setting command signal, and for adjusting the orifice of the flow control valve so as to maintain a predetermined flow rate. The flow-rate setting command signal is prescribed according to an amount of gas supply necessary for the plasma processing.
With the plasma processing apparatus of the prior art equipped with a mass flow controller of the above-described structure, however, there has been a problem in the gas supply during the plasma processing.
That is, in the past, the mass flow controller has been provided with a prescribed flow-rate setting command signal as described above, when supplying the gas into the processing chamber of which an interior is evacuated to a vacuum state. As the flow rate is set, an upstream gas shutoff valve is opened, and the processing gas is delivered toward the mass flow controller from a gas supply source such as a gas cylinder or the like.
The feedback controller regulates the flow control valve in a manner to expand the orifice in an attempt to increase a flow rate of the gas to a flow rate closer to the prescribed flow rate, since the flow rate of the gas at the flow rate detector of the mass flow controller is zero before the gas shut-off valve is opened. When the gas shut-off valve is opened under this condition, an excessive amount, or well over an appropriate amount of the processing gas actually needed, is supplied into the processing chamber, because the gas is supplied with the flow control valve open excessively. This results in a substantial increase in pressure of the processing chamber, thereby requiring a long period of gas evacuation in order to bring the pressure in the processing chamber to a proper level for starting the plasma discharge. In other words, it needlessly increases a time from a beginning of the vacuum evacuation to the start of plasma discharge, and causes a delay of cycle time.
The present invention is to provide a plasma processing apparatus as well as a method of plasma processing that can shorten a time required for vacuum evacuation and improve productivity.
The plasma processing apparatus of this invention is intended to carry out plasma processing on a work object, and it comprises:
a processing chamber for enclosing the work object to be processed and for carrying out plasma processing;
evacuation means for evacuating an interior of the processing chamber to a vacuum state;
a gas importing unit for supplying processing gas to the processing chamber through a gas supply passage, the gas importing unit comprising
a gas shut-off valve for opening and/or closing the gas supply passage to be connected to a supply source of the processing gas,
a flow rate detector for detecting a flow rate of the processing gas in the gas supply passage,
a flow control valve disposed in the gas supply passage, and provided with an adjustable orifice opening, and
a main controller for outputting a flow-rate setting command signal, and controlling opening and/or closing of the gas shut-off valve;
a plasma generator for generating plasma in the interior of the processing chamber; and
wherein a feedback controller is operably coupled to the flow control valve and the flow rate detector for controlling the orifice of the flow control valve according to the flow-rate setting command signal, and according to a result of the flow rate detected by the flow rate detector.
Also, a method of plasma processing of this invention employs the above-said plasma processing device, and it includes a gas supply step for producing an output of a flow-rate setting command signal, for setting a flow rate to zero, prior to opening the gas shut-off valve, and another flow-rate setting command signal for setting a predetermined flow rate only after the gas shut-off valve is opened.